Stay cables may be used for supporting bridge decks, for example, and may typically be held in tension between an upper anchorage, secured to a tower of the bridge, and a lower anchorage, secured to the bridge deck. A cable may comprise dozens or scores of strands, with each strand comprising multiple (eg 7) steel wires. Each strand is typically retained individually in each anchorage by tapered conical wedges, seated in a conical hole in an anchor block. Tensioning of the strands can be performed from either end, for example using hydraulic jacks. When in use, cables may be subjected to lateral, axial and/or torsional forces due to vibration or other movement of the bridge deck (which may arise due to wind, or to the passing of heavy traffic, for example). As a result of the above effects, the cables may experience lateral, axial and/or torsional oscillatory motion. This oscillatory motion may be in the cable as a whole (ie the strands of the cable moving together), or it may be in individual strands, or both. Other cables, such as pre-stressing cables, may also be subject to static and/or dynamic deflection at or near the end anchorages.
Such oscillatory movements in a cable, strand or wire may result in damages of the individual strands and of the anchorage, due to repeated impacts between the strand and strand channel, and due to bending stress notably where the strands are anchored. This friction between strand and strand channel can, over time, cause fretting, work-hardening or other damage to the cable and/or to the anchorages, thereby significantly reducing the serviceable life of the cable and/or anchorage, and greatly increasing the maintenance and monitoring effort required. Replacing damaged strands is a time-consuming and expensive operation and usually entails significant interruption of traffic in the case of a bridge. This is particularly so if all of the strands in a cable must be replaced at once.